Field
This application relates generally to wireless communication and more specifically, but not exclusively, to determining a parameter to be transmitted by an access point.
Introduction
A wireless communication network may be deployed over a defined geographical area to provide various types of services (e.g., voice, data, multimedia services, etc.) to users within that geographical area. In a typical implementation, macro access points (e.g., each of which provides service via one or more cells) are distributed throughout a macro network to provide wireless connectivity for access terminals (e.g., cell phones) that are operating within the geographical area served by the macro network. A macro network deployment is carefully planned, designed and implemented to offer good coverage over the geographical region. Such a careful planning cannot, however, completely accommodate channel characteristics such as path loss, fading, multipath, shadowing, and so on, in indoor environments. Indoor users, therefore, often face coverage issues (e.g., call outages, quality degradation) resulting in poor user experiences.
To supplement conventional network access points (e.g., macro access points), small-coverage access points may be deployed (e.g., installed in a user's home) to provide more robust indoor wireless coverage or other coverage for access terminals. Such small-coverage access points may be referred to as, for example, femto access points, femto cells, home NodeBs, home eNodeBs, or access point base stations. Typically, such small-coverage access points are connected to the Internet and the mobile operator's network via a DSL router or a cable modem. For convenience, small-coverage access points may be referred to as femto cells or femto access points in the discussion that follows.
An unplanned deployment of large numbers of femto cells may present various operational issues. As one example, issues may arise for mobility management of an access terminal between a macro network and a femto cell. Here, as an access terminal roams throughout the geographical area associated with a network, signal conditions for the access terminal within a given cell may deteriorate, whereby the access terminal may be better served by another cell (e.g., access point) in the network. That is, it may be desirable for the access terminal to reselect to another cell in idle mode or be handed-over to another cell in active mode. A typical example would be where a mobile subscriber currently served by a macro cell comes to a location (e.g., the subscriber's home) where a femto cell for that subscriber is deployed, or where a mobile subscriber currently served by a femto cell leaves the coverage of the femto cell and needs to acquire service from the macro cell.
To facilitate such mobility, an access terminal regularly monitors for signals (e.g., beacon/pilot signals) of nearby cells. These signals are then compared to determine whether the access terminal should remain on its current serving cell or switch to another cell. In practice, one or more parameters may be used to control how aggressively (e.g., under what signal conditions) an access terminal performs searches for other cells. In addition, one or more parameters may be used to control when (e.g., under what signal conditions) an access terminal re-selects to another cell or is handed-over to another cell.
For example, macro system information block (SIB) settings such as SIB3 and SIB11 may be set to ensure good femto cell discovery performance and avoid unnecessary registration attempts by macro access terminals (e.g., access terminals that are not authorized for access at the femto cell). Once an access terminal is camped on a femto cell, the access terminal uses SIB settings broadcast by the femto cell for idle cell reselection. Hence, the femto cell SIB parameters (e.g., SIB3 and SIB11) also may be set to provide good performance for home access terminals (e.g., access terminals that are authorized for access at the femto cell). In particular, it may be desirable to set the SIB parameters of the femto cell such that a home access terminal reselects to a macro cell in a timely manner as the home access terminal leaves the femto cell coverage so that the access terminal does not go into outage. Moreover, it also may be desirable to avoid ping-ponging effects between the femto cell and the macro cell (e.g., an access terminal reselecting back and forth between the femto cell and the macro cell). Timely reselection to the macro cell and avoiding ping-pong effects between the femto cell and the macro cell may improve performance in terms of missed pages, call drops, and access terminal battery life.
For an access terminal that obeys search thresholds (e.g., Sintrasearch and Sintersearch), the search thresholds broadcast by a femto cell may be set relatively low such that the access terminal performs searches only when the signal quality on the femto cell is relatively low (e.g., when Ecp/I0<−15 dB). This may avoid possible ping-ponging between the femto cell and the macro cell, especially near the macro cell site where the macro Ecp/I0 is relatively high. At the same time, the Qhyst parameter broadcast by the femto cell may be set to a low value (e.g., 2 dB) to ensure timely cell reselection from the femto cell to the macro cell, especially when the femto cell is located at the macro cell edge where macro Ecp/I0 is relatively low.
However, some access terminals may perform searches irrespective of search thresholds. For these access terminals, the Sintrasearch and Sintersearch parameters may not be of use for avoiding the above ping-pong effect.